2941
Land reclamation on soft clays at Port of Brisbane
Construction d’un terre-plein sur des sols argileux dans le port de Brisbane
Ganesalingam D., Sivakugan N.
School of Engineering and Physical Sciences, James Cook University, Australia.
Ameratunga J.
Coffey Geotechnics, Brisbane, Australia.
Schweitzer G.
Port of Brisbane Pty Ltd, Brisbane, Australia.
ABSTRACT: Land reclamation work is being carried out for the Port of Brisbane (PoB) Future Port Expansion Project, in the State of
Queensland, Australia, which would develop a new reclaimed area of 235 ha. The mud excavated during maintenance dredging
operations is pumped into the containment paddocks within the reclamation area. The dredged mud is soft and fine grained in nature,
placed in a remoulded dilute slurry form at water content of at least 200%. The reclamation site is underlain by weak Holocene clays
of depths up to 30 m. With such a large compressible thickness of both dredged fill and the underlying in situ Holocene clays, the
total settlement under development loads during the primary consolidation will be significant. The secondary compression will be
another considerable component of settlement to deal with. This paper briefly addresses the maintenance dredging works and the
background of the PoB land reclamation project. It mainly focuses on the site conditions, the design of surcharge loading and
installation of vertical drains to accelerate the consolidation settlement and minimize the post construction secondary compression.
Furthermore, the in-situ and laboratory tests undertaken and the soil parameters obtained from these tests are discussed along with
empirical correlations used to estimate appropriate soil parameters.
RÉSUMÉ : Des travaux d’aménagement s’inscrivant dans le cadre du « Future Port Expansion Project » (Projet d’extension du futur
port) sont menés dans le Port de Brisbane, dans l’Etat du Queensland en Australie. Ce projet prévoit la création d’une étendue de terre
de 235 ha gagnées sur l’eau. Les boues issues des opérations de dragage de maintenance sont pompées vers des bassins au sein même
de la zone aménagée. Ces boues naturellement molles et fines forment une suspension diluée contenant au minimum 200% d’eau. Le
site repose sur des terres argileuses datant de l’Holocène sur une profondeur allant jusqu’à 30 m. Avec une telle épaisseur d’argile
compressible d’origine in-situ ou provenant du dragage, le tassement total dû aux charges de développement lors de la consolidation
primaire sera significative. La compression secondaire constituera une composante supplémentaire à prendre en compte pour le
tassement. L’article présente brièvement les travaux de dragage de maintenance et le contexte du projet de terre-plein dans le Port de
Brisbane. Il se concentre principalement sur les caractéristiques du site, la conception des suppléments de charge et l’installation de
drains verticaux pour accélérer la consolidation de l’installation et minimiser la compression secondaire liée à la construction. Les
tests menés en laboratoire et sur le site ainsi que les paramètres du sol obtenus à partir de ces tests, et les corrélations empiriques
utilisées pour estimer ces paramètres sont également abordés.
KEYWORDS: land reclamation, dredged mud, sedimentation, consolidation, vertical drains
1 INTRODUCTION
Dredging and land reclamation is a billion dollar industry
asscociated with the ports throughout the coastal region of
Australia. Maintenance dredging is carried out regularly in
many major Australian ports and in some cases the dredged
mud is reused as filling materials in the land reclamation works
undertaken near the coast. The land reclamation works carried
out in the Port of Brisbane (PoB) expansion project, Australia is
one of the examples.
The Port of Brisbane is located at the mouth of the Brisbane
River at Fisherman Islands, and it is the major port in the state
of Queensland, Australia. In order to expand the port to
accommodate additional facilities to meet the development
expected in the next 25 years, the Port of Brisbane has
embarked on a land reclamation process adjacent to the existing
land mass, which will ultimately see 235 ha of new reclaimed
land area, at the completion of the project. The 4.6 km long rock
and sand seawall constructed around the perimeter of the site in
Moreton Bay bounds the area which is being reclaimed
(Ameratunga et al. 2010a). The seawall extends up to 1.8 km
into Moreton Bay (Fig.1).
Annually around 300,000 m
3
of mud is extracted from the
adjacent Brisbane River during the maintenance dredging works
carried out in the navigation channel and berths. Land
reclamation is undertaken by reusing these dredged materials in
an environmentally friendly manner, as a way of disposing the
dredged mud. The reclamation area is partitioned into a number
of containment paddocks. Dredged mud is pumped into the
containment paddocks in a slurry form of water content of at
least 200 % and allowed to undergo self weight consolidation.
The height of the dredged mud placement varies from 7 m to 9
m.
Dredged mud is a weak, fine grained soil with predominantly
40% silt and 50% clay constituents. The dredged mud fill is
underlain by highly compressible in-situ Holocene clays, with
thickness varying from 9 m to as much as 30 m. Since both in-
situ clays and dredged mud are highly compressible and have
low permeability characteristics, they are treated with
preloading together with vertical drains to accelerate the
consolidation process. Selecting appropriate soil properties is
essential for reliable prediction of the degree of consolidation
and future settlements. Hence, both horizontal and vertical
consolidation parameters are required when vertical drains are
used.
The paper outlines the land reclamation works with the
design of preloading and vertical drains. Detailed review of the
design strength, consolidation and compressibility parameters
